Hey,
Remember me??
I've used UnderCover for well over 17 years. My double bass bag has ample room for two 6 strings. What I like most about these bags over other more modern offerings is that Undercover offers two big and spacious pockets for your gear. I stuff so much gear into mine I'm shocked that they don't rip open sooner.
I've owned 2-3 Undercover double bags over the last 17 years or so. I gig a lot, more than most bass players, and do a fair amount of road work where the bag endures bumpy van rides sitting on top of other gear. The bags have held up remarkably well, enough for me to easily want to buy another one when this one wears out.
Good luck.